As typical transparent resins, there are known polymethyl methacrylate (PMMA), polycarbonates (PC), polyethylene terephthalate (PET), epoxy resins, polyethylene (PE), polypropylene (PP) and the like. However, these resins have a refractive index of about 1.60 at the maximum.
On the other hand, the present inventors have already found the novel sulfur-containing compounds having an episulfide structure, and have developed transparent resins having a refractive index of 1.71 which is far higher than those of the conventionally existing resins (refer to JP 9-71580A and JP 9-110979A). In these previous inventions made by the present inventors, the sulfur-containing compounds having an episulfide structure are cast into a so-called mold and then polymerized and cured to obtain a cured product thereof. However, these methods are limited only to production of lenses or substrates themselves. Nevertheless, owing to the remarkable high refractive index of the transparent resins, there is a strong demand for applying the transparent resins to coating materials for various substrates or films.
However, since coating materials made of the transparent resins generally exhibit a poor wetting property to various substrates, it is difficult to stably form a thin film having a thickness of from several μm to several tens μm.
As an example of film-like cured products made of thiirane ring-containing compounds, there are disclosed rapid-curing adhesives for electronic materials (refer to JP 11-209686A, PCT Pamphlet WO 00/46317 and JP 2002-173533A). However, these conventional adhesives all require further addition of curing agents such as epoxy-based and amine-based curing agents to enhance a peel strength of the resultant cured products. Further, the above related documents have failed to specify a refractive index, a discoloration, a transparency and a uniformity of the adhesives, since the object thereof is not to study and improve these properties.
In addition, there have been proposed compositions composed of the thiirane ring-containing compound and a silane coupling agent, for example, spectacle lens compositions (refer to JP 10-298287A) and dental opaque coatings (refer to JP 2003-89759). However, JP 10-298287A describes no effect obtained by addition of the silane coupling agent, though it is deemed that the silane coupling agent is added to control close contact between the lens and a glass mold. Also, in JP 10-298287A, a massive cured lens is finally released from the glass mold to achieve the object aimed by the invention. Thus, the invention described in JP 10-298287A is quite different in technical concept from the present invention which is intended to improve the adhesion property, and aims to produce film-like optical products bonded to a substrate.
Also, JP 2003-89759A describes thiirane ring-containing compounds merely as an example of polymerizable monomers, and fails to provide specific embodiments or examples using the thiirane ring-containing compounds. Further, in JP 2003-89759A, (meth)acrylic compounds are specified as the polymerizable monomers, and in order to satisfy the coating performance, it is required to use may other components such as fluorocarbon group-containing polymerizable monomers. In addition, the coating film described in JP 2003-89759A is used for dental purposes and, therefore, is required to exhibit a high hiding property. Thus, the invention described in JP 2003-89759A is also quite different in technical concept from the present invention seeking a high transparency.
An object of the present invention is to provide coating compositions capable of forming a coating film having a high refractive index, a less discoloration, and excellent transparency, uniformity and adhesion property when polymerized and cured; coating films produced from the composition; and optical products provided on a surface thereof with the coating film.